A flat conductor wire is used as a wire forming a coil in order to enhance the space factor of the coil in a motor. The space factor in this description indicates a ratio of the cross-sectional area of a wire to the cross section of a space in which the coil is placed. However, the flat conductor wire has a large cross-sectional area. Thus, when the flat conductor wire is placed in an alternating magnetic field, large eddy currents tend to occur in a surface perpendicular to magnetic fluxes in the flat conductor wire. This may increase eddy current loss. This eddy current loss is power loss caused by the flow of eddy currents.
Therefore, it is conceivable that a plurality of thin conductor wires (hereinafter, referred to as “fine wires”) having an insulating part such as enamel, oxide, etc. formed on an outer peripheral surface is bound in a bundle to reduce the cross-sectional area of each conductor wire, thereby reducing eddy currents to decrease the eddy current loss.
As a conventional technique of binding a plurality of the fine wires in a bundle, a conductor wire is proposed in which the fine wires are assembled in a bundle and a resin coating is formed on the outer peripheral surface of this bundle of fine wires by extrusion to maintain the assembled condition of the fine wires.
However, the outer peripheral surface of the bundle of fine wires is coated with resin and thus a coating part is low in strength. For example, when a conductor wire is bent to form a coil for motor and the bending radius of each bend (each curved portion) of the conductor wire becomes different between the inside fine wire and the outside fine wire, causing a difference in circumferential length, the fine wires could not maintained in the assembly state by the resin coating. The fine wires tied in a bundle will come apart.
Herein, Patent Literature 1 discloses a compound winding in which a plurality of flat insulating wires are stacked and provided with a common insulating layer on an outer peripheral surface of the assembly.